Previous experiments have shown that the two glutaminase isoenzymes have a nearly complementary distribution in the various tubular structures of the kidney, that in response to acidosis only the phosphate dependent glutaminase (PDG) increases in activity and that this increase occurs only in proximal convoluted tubules. Both isoenzymes are particulate and we have also determined their subcellular distribution. PDG was shown to be contained in the inner mitochondrial membrane and the phosphate independent glutaminase (PIG), is contained on the brush border membrane. PDG undergoes extensive polymerization in the presence of borate. This phenomenon has been used to purify PDG (3000 fold) after solubilization from mitochondria to near homogeneity by successive gel filtration in each of its molecular weight forms. The different forms also exhibit different kinetic properties. The conditions necessary for this association dissociation process and the properties of the different forms are under investigation in an effort to determine if they contribute to its physiological regulation. PIG can be solubilized by treatment with detergents and its purification is now being attempted. Its kinetic and physical characterization will be undertaken in order to determine its possible mode of regulation. Immunological experiments have shown that increased PDG activity during acidosis is due to increased amount of PDG. We are currently developing a scheme for the isolation of proximal convoluted tubule cells. Such a preparation should offer a system in which we can compare glutamine uptake, PDG activity and ammonia synthesis.